Ninja was a job that was added later on, and at first glance it looks like there is no significant change to the basics of their battle capabilities.
On the attack side of things, there will be a new third part of the combo from Spinning Edge and Gust Slash. The weapon skill that serves as the third stage of the new combo will also have a combo additional effect to prolong the effect duration of Huton. Previously, ninjutsu would often be used to recast Huton, so because this makes room for other ninjutsu, there could be a major change with the ability to use more than one ninjutsu.
You'll have to look over your rotation completely since you'll also need to continue to maintain the two DoTs and skills which weaken enemies.
Additionally, there will also be an action allows a single weapon skill to hit three times, so by pairing this with abilities which increase damage for an effect duration it should become possible to put out some impressive DPS.
Two of the new actions will be support abilities. One ability will allow the ninja to pass on the majority of their accumulated enmity to a party member. It was a common sight to have Shukuchi pull hate instead of a tank at the start of a fight, so this might be something you can utilize instead of intentionally stopping DPS to allow the tank to get control of enmity. There will be another action which has the effect of reducing the target's enmity. It can be used on other party members, so it might be quite useful.
With the new three stage combo and the other added support functions, it seems like Ninja will be a bit more tricky to play as a DPS and will also need to more consciously cooperate with its party to have the greatest impact.